It is an elective course where the basic theory of seismic wave propagation, the modern methods and results regarding the investigation of the Earth's interior through natural seismic sources, i.e. earthquakes, are presented.
Introduction to the exploration of the Earth's interior: basic concepts, historical review of the evolution of knowledge about the Earth's structure; Propagation of elastic seismic waves in the Earth's interior: elasticity theory, types and properties of seismic waves, wave-fronts, seismic ray theory, Fermat's principle, Snell's law, Huygens' principle, reflection, refraction, diffraction, head-waves, ray parameter, polarization of particle motion, wave transformations; Identification of discontinuities in the Earth's interior: seismic wave travel-time curves, phase triplication effect, caustics, low-velocity zone, Earth's core shadow zone; Structure of the Earth: distinction of crustal types (continental, oceanic), lithosphere, asthenosphere, upper/lower mantle, transition zone, D” layer, outer/inner core, one-dimensional models of the Earth for seismic wave propagation velocities, changes in physical properties and mineral composition with depth, nomenclature of major discontinuities, nomenclature of seismic phases; Rayleigh and Love surface waves: propagation and properties of surface waves, phase and group velocity, dispersion effect, methods of measuring phase/group velocities, construction of 1D shear-wave velocity models from dispersion curves, global propagation of surface waves; Seismic tomography: categorization by data type and study scale, the forward and inverse problems, parameterization of tomographic inversion, synthetic tests, reliability assessment of results, construction of 3D velocity models; Interpretation of tomographic models: identification of velocity anomalies at global, regional and local scales, interpretation of velocity anomalies as a function of depth, mantle tomography, mid-ocean ridges, subducting plates, hot spots/mantle plumes, tomography in fault zones, tomography in volcanic environments, evaluation of the resolution of tomographic models; Surface wave tomography: the cross-correlation function, waveform stacking, Eikonal tomography (apparent phase velocity), multi-pathing effects, Helmholtz tomography (structural velocity), ambient noise tomography, examples of applications; Seismic anisotropy: physical causes of seismic anisotropy, shear-wave splitting (SWS) effect, methods of measuring the splitting parameters in S and SKS waves, anisotropy in the upper crust, anisotropy in the upper mantle, relation between SWS parameters and mantle flow; The D” layer: lower mantle tomography, large low velocity shear-wave velocity provinces (LLSVP), ultra-low velocity zones (ULVZ), anisotropy and scattering phenomena at the base of the lower mantle, methods of structure determination in the D” layer, interpretation of observations; Receiver functions method: convolution and deconvolution, the H-k stacking method (crustal thickness and Vp/Vs velocity ratio), back-projection of receiver functions at depth, common conversion point stacking technique, applications to determine the depth of major discontinuities (Moho discontinuity, lithosphere-asthenosphere boundary, discontinuities in the transition zone, discontinuities related to subducting plates); Velocity spectrum analysis (vespagrams), brief introduction to seismic arrays, detection of weak amplitude seismic phases.